1. Field of the Invention
The present invention relates to a method of production control and a method of manufacturing industrial products and, more particularly, to a method of production control and a method of manufacturing industrial products which are preferably used for the manufacture of electronic apparatus such as liquid crystal displays.
2. Description of the Related Art
A method of production referred to as a “Kanban system” is known as a method for eliminating wasteful work in process and centralizing flows of information (see Non-Patent Document 1 for example). In a Kanban system, units required at a process are withdrawn from the preceding process in the quantity of units which have been used at the subsequent process, and the unit is replenished at the preceding process in the quantity of the units withdrawn, which allows the production to be performed on a “just-in-time” basis. What is important for a Kanban system is that production-ordering Kanbans for a process accompany physical units without fail and that units are produced in quantities shown on Kanbans which have been detached and in the order in which the Kanbans have been detached.
It is a prerequisite for the Kanban system that the types and quantities of products to be produced are smoothed in making a monthly production plan and production capacity plan so that production will be continuously performed at a constant daily rate. When there are significant demand changes or when a great batch of products of the same type is produced during a setup change, product types to be produced or the ratio between the product types may change every day. In such a case, a determination cannot be made on when to launch a product even if a Kanban for the product is detached or whether to launch a product before a Kanban for the product is detached. A problem therefore arises in that it is difficult to use the Kanban system in such a case.
In the case of the Kanban system, since a processing target for even a bottleneck process or restricted process is determined by the number of Kanbans and the progress of processing at the subsequent process, a problem arises in that the bottleneck process or restricted process cannot necessarily be run to its maximum capacity. Further, when there is a plurality of bottleneck processes or restricted processes, since the stoppage of processing at a subsequent bottleneck has influence on processing at a preceding bottleneck, a problem arises in that the throughput of the entire production line cannot be improved.
Furthermore, in the case of a production line which has not been smoothed with respect to the types and quantities of products, it may sometimes be difficult to achieve an initial production plan only through a comparison between the actual production and the plan because of not only demand changes but also various disturbances that may occur on the production line. Another problem is that there is no method of production control which is effective in such a case. In particular, when a forecast is revised, it is difficult to make a comprehensive evaluation of production by evaluating production of each product type. No effective index for evaluation has been available in such a case.
A significant problem arises in the Kanban system when a process requiring a long time for a setup change is a bottleneck process or restricted process. In such a case, a required quantity cannot be processed without reducing the number of setup changes. Such a production line is under limitations such as the fact that a required quantity of products cannot be achieved without processing the single product type for one day or more, and a problem therefore arises even when Kanbans are used in that production cannot be started in accordance with Kanbans which have been detached.
When outputs from a plurality of production lines manufacturing parts and half-finished products are supplied to a combining line or aligning line, if the production lines are not smoothed in terms of types and quantities of the parts and products, a problem arises in that it is difficult to make a production plan on the basis of the pull system because no effective method of production control exists for such production lines.
Patent Document 1: JP-A-2001-273023
Patent Document 2: JP-A-2002-244708
Patent Document 3: JP-A-2004-152052
Patent Document 4: JP-A-2001-273021
Patent Document 5: JP-A-8-25191
Non-Patent Document 1: “Seisan Kanri ga Wakaru Jiten”, Nippon Jitsugyo Publishing Co., Ltd., Tadami Sugamata and Kazunari Tanaka, March 1986, p. 301